Feathers flying over wind-farm project

Tuesday

Oct 30, 2007 at 12:01 AMOct 30, 2007 at 7:38 AM

The specter of piles of dead birds has been an issue with wind-farm projects, including those in Yates and Steuben counties. A study should allay some fears and provide deep insights into nocturnal bird flight.

Rich Eldred

Watchdog groups protesting wind turbine projects in Cohocton, Italy and Prattsburgh have listed the threat to birds as one of the reasons not to put up turbines here.

Tall towers and turbines have always taken a high toll on avian life when placed in the path of migrating birds. But recent research indicates that the number of bird deaths caused by fly-ins with tall towers is decreasing.

One 1,000-foot television tower in Eau Claire, Wis., killed 12,000 birds in one night. During a 42-year period, 121,000 deaths were documented. However, while 2,000 birds a year from the 1960s to the 1980s were the average, that number has now toppled to fewer than 100. Have the birds wised up, or perhaps the number winging that flyway has fallen so low that only a few flutter past the lethal tower?

Bill Evans, a pioneer in using acoustic data to track the night flights of migrating birds, has pondered these questions for decades. Recently, he shared his thoughts with a rapt audience at Wellfleet Bay Wildlife Sanctuary on Cape Cod. Offshore turbines have been proposed for the cape.

“I’ve been studying avian nocturnal migration for 22 years,” Evans explained. “On a good night inland, you can hear thousands of calls.”

He founded the acoustic night-flight research program at Cornell University in the 1990s, and it remains based in upstate New York. Initially, he was tracking and identifying species by their chirps from far overhead. In 1996, he was working for Nebraska Public Power, assessing a proposed turbine project and its possible impact on Baird’s sparrows.

“I was looking for a source of power for a VCR; I ran a mike into that and eight hours of sound,” he recalled. “The site had a 300-foot radio tower on the Great Plains. Every night, I was recording sound from the sky near the tower and counting flight calls. One thing I found, I recorded some collisions with the tower, so that opened my eyes that even a short man-made structure can kill migrating birds.”

Night migrating birds fly high. Those 1,000-foot towers poke up into their path, but shorter towers should have been below their altitude. With radio, then TV, cell phones and wireless Internet towers are sprouting like pine trees. In Massachusetts, as of 2004, there were 11 towers over 800 feet, 143 between 200-299, 61 from 300-399, 20 from 400-499 and 16 between 500-799 feet. A couple of those 500-footers are on the Upper Cape.

Those towers are lit so that airplanes can avoid them, but those lights may be attracting birds.

“Research suggests flashing lights are much safer for birds than any permanent lights,” Evans noted. “But if you have a low cloud ceiling, any bright light source leads to bird aggregation and congregation. Eastern North America has been lit up the last 50 years. Most migration is on clear nights, but when there is a low cloud ceiling, birds appear disoriented by light.”

Studies revealed that birds were more attracted to short wavelength light (blues, greens) than long (red). Most towers are lit with red lights, so that should be good.

O“But the birds migrating at night use their cones (as opposed to rods in the eyes) that are less sensitive to red light,” Evans noted. “It could be they just don’t see the red lights (and hit the tower or guy wires). That’s one theory.”

Flying at night has several advantages: The birds can rest during the heat of the day and feed; they use less energy flying when it is cooler; they avoid predators; the air is less turbulent; and they can utilize celestial navigation.

“Another theory is that birds sense the earth’s magnetic field, and that’s how they tell north from south when they can’t see the stars,” Evans said. “But that is a light-dependent mechanism. Birds in a box, with no light, can’t tell which way is north or south but given a little light, they can. But if it’s only shortwave light (red), they can’t.”

Tests using halogen lights have shown that continuous lights will draw birds in and cause aggregation, but if they blink or go off for a time, the birds move on.

Wind turbines are a new hazard. A study at the Maple Ridge wind farm on the Tug Hill plateau in New York, where there are 195 400-foot turbines, found the estimated toll, by carcass count, was 125 birds of 30 species and 326 bats over a span of several months. Most of those were killed while migrating at night; 326 bats were also found. Extrapolated over the full farm for the full season, the numbers were 1,150 birds and 3,000 bats.

Other projects have higher estimates of 100 birds per turbine.

“Some are killing more birds than others,” Evans noted. “Geographic location is the big variable. The rate of passage of night-migrating birds is a key factor as well.”

Ideally, it wouldn’t be necessary to build the project to determine its effect.

“We’d like to forecast what the mortality will be at a wind site before it is built, but we don’t actually know,” Evans admitted. “The general concept has been to steer wind power to areas where there are not migrating birds.”

While Evans uses acoustics to monitor migration, Doppler radar can also be used, with less precision. Radar has been used to estimate the migratory levels in Nantucket Sound. A study found 154.5 “pings” per kilometer per hour, which is on the low end. New York, Pennsylvania and West Virginia sites ranged from 116 to 509. But indications were that 66.5 percent of the birds were flying below turbine height, which is much greater than the inland locations (20 percent to 29 percent).

“One would predict the mortality would be higher at a wind project in the mid Atlantic than in inland western New York and that the annual mortality would vary by 500 percent in the mid Atlantic depending on location,” Evans said.

Evans has noticed that in New York, migration was spread out on clear nights, but the birds “clustered” in valleys on cloudy nights.

“It is worth doing research on these patterns to minimize mortality,” he observed.

In the case of an offshore project, such as Cape Wind, you can just collect the dead birds on the ground to monitor its impact.

“If Cape Wind is built, we’ll have no way to know what it kills,” Evans said. “We need some way to do this. Europeans are using acoustics (recording collisions) but haven’t published their results, suggesting they are having problems with it.”